This invention relates to a hydraulic tilt device for a marine propulsion unit and more particularly to an improved hydraulic arrangement for such a device that permits more rapid operation than was possible with prior art devices.
In most hydraulically operated tilt and trim units for marine outboard drives, at least one double acting fluid motor is provided for powering the outboard drive between its tilted up and its tilted down positions. This hydraulic mortor is operated by means of a reversible fluid pump that selectively supplies fluid under pressure to one side of the fluid motor and vents the other side back to the port of the fluid pump that is acting as the suction port. Although fast operation is always desirable, there is a practical limit to the speed at which the outboard drive can be tilted up. If the outboard drive is tilted up too rapidly, the reactive force on the associated watercraft tends to cause its bow to rise and too rapid an elevation can result in a dangerous situation. As a result, the hydraulic circuitry and the output of the fluid pump is governed so as to restrict the rate of elevation to about 2.degree. of tilting per second.
With the hydraulic systems of the type previously proposed, however, all of the fluid that is displaced from the non-pressurized side of the fluid motor is returned back to the pump circuit through the port of the fluid pump that is acting as the suction port. Thus, if the system is designed so as to limit the rate at which the outboard drive may be tilted up, the tilting down rate is also so controlled. However, the reasons which make it desirable to limit the tilting up speed of the outboard drive do not apply equally to tilting down operation. In fact, there are many instances when it is desirable from a safety and operational standpoint to effect tilting down at a much more rapid rate than tilting up. For the reasons noted above, however, the prior art systems have not permitted such rapid titlting down operation.
It is, therefore, a principal object of this invention to provide an improved hydraulic tilt and trim unit for a marine outboard drive.
It is a further object of this invention to provide a marine outboard drive hydraulically operated tilt and trim unit that permits more rapid ilting down operation than tilting up operation.
It is yet a further object of this invention to provide a hydraulic tilt and trim unit for a marine outboard drive in which the return fluid from the hydraulic tilt cylinder need not pass through the suction side of the powering fluid pump.